Influenza vaccination programs, which cost nations millions of dollars every year, could be a waste of time and money, says Dr. Tom Jefferson, Cochrane Vaccines Field, Rome, Italy. Jefferson says he hopes his findings will make North American and European taxpayers wonder whether the effort and expense are justified.

You can read about his findings in The British Medical Journal (BMJ), October 28.

In this study, Jefferson examined all published papers worldwide that reported on the effects of inactivated vaccines (vaccines with dead viruses). In other words, he studied the reviews of all studies. He concluded that flu shot campaigns have either no effect, or a very negligible effect, on the number of hospitalizations, work/school time lost, complications from flu, or death from flu.

Jefferson said "I looked at the evidence described by systematic reviews and confronted it with policy and I found that there is a massive gap. Almost none of the benefits that these policy documents list are actually given by inactivated vaccines or, if they are, they are given in slighter measure." He said he is not sure why this is so. He suggested it could be a result of inadequate surveillance systems, and/or diagnosing too many influenza-like respiratory illnesses as flu (when they are not). He added that "In most surveillance systems, you actually have an almost year-round epidemic which, in fact, is not influenza. It's caused by other agents." He criticized many of the studies he looked through, saying they were weak.

According to official figures (CDC), approximately 200,000 Americans get flu so badly each year that they have to be hospitalized - about 36,000 people die each year as a result of catching flu in the USA.

Jefferson said he was surprised to see such a large gap between vaccination campaign policy and evidence of its effectiveness.

Each year enormous effort goes into producing influenza vaccines for that specific year and delivering them to appropriate sections of the population. Is this effort justified?

Viral infections of the respiratory tract impose a high burden on society. In the last half of the 20th century, efforts to prevent or minimise their impact centred on the use of influenza vaccines. Each year enormous effort goes into producing that year's vaccine and delivering it to appropriate sections of the population. Here, I will discuss policies on the use of inactivated vaccines for seasonal influenza; the evidence for their efficacy, effectiveness, and safety ("effects"); and possible reasons for the gap between policy and evidence.

Policies

Every vaccination campaign has stated aims against which its effects must be measured. The US Advisory Committee on Immunisation Practices produces a regularly updated rationale for vaccination against influenza.1 The current version identifies 11 categories of patients at high risk of complications from influenza (box).

The rationale rests on the heavy burden that influenza imposes on the population and the benefits of vaccination. For example, reductions in cases, admissions to hospital, mortality of elderly people in families with children, contacts with healthcare professionals, antibiotic prescriptions, and absenteeism for children and household contacts are the main arguments for extending vaccination to healthy children aged 6-23 months in the United States.2 Canada introduced a similar policy in 2004.3 Less comprehensive policies recommending vaccination for all people aged 60 or 65 and over are in place in 40 of 51 developed or rapidly developing countries.4 On the basis of single studies, the World Health Organization estimates that "vaccination of the elderly reduces the risk of serious complications or of death by 70-85%."5 Given the global nature of these recommendations, what type of evidence should we expect to support them and what does available evidence tell us?4

Which evidence?

When considering the best evidence for vaccination we must take into account the unique epidemiological features of influenza viruses and the rationale for immunisation. The incidence and circulation of seasonal influenza and other respiratory viruses vary greatly each year, each season, and even in each setting. A systematic review of the incidence of influenza in people up to 19 years' old reported a seasonal variability of 0-46%; during a five year period the average incidence was 4.6% in this age group. During a period of 25 years the incidence was 9.5% in children under 5.6 Because of this variability and lack of carryover protection from one year's vaccine to the next,7 especially if the virus changes its antigenic configuration, single studies reporting data from one or two seasons are difficult to interpret. Single studies are also not reliable sources for generalising and forecasting the effects of vaccines, especially when numbers are small. They introduce further instability into already problematic forecasting. Additional limitations to our forecasting ability are imposed by our use (and misuse) of studies assessing the effects of influenza vaccines. Although the effect assessed depends on the aims of the particular campaign, most concentrate on serious effects (such as pneumonia or death) and person to person transmission (table 1). Field efficacy studies are only relevant when viral circulation is high, but no one can forecast with precision the impact on next year's influenza.